Almost every home battery arrives with an impressive headline: a 10-year warranty. Some manufacturers now promise 12 or even 15 years. But that headline doesn’t always tell the whole story.
- What does a 10-year battery warranty actually cover?
- Batteries age in two different ways
- What is a battery cycle?
- What is battery throughput?
- Could you reach the throughput limit before 10 years?
- How to estimate your own battery’s throughput period
- When should homeowners pay particular attention?
- Is the Tesla Powerwall 3 different?
- Does this mean 10-year battery warranties are misleading?
Buried in the warranty documents of many batteries is a second limit - one based on how much energy passes through the battery during its lifetime. If you reach that limit before the advertised number of years has elapsed, part of your warranty cover may be affected.
It’s similar to a car warranty covering you for a set number of years or a maximum mileage, whichever comes first.
The difference is that car manufacturers put the mileage limit front and centre. With batteries, the equivalent number - known as energy throughput - can be much harder to find.
So, could the way you use your battery cause you to reach its warranty limit early? Here’s what homeowners need to know.
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What does a 10-year battery warranty actually cover?
Battery warranties vary, but they commonly include two separate promises:
A product warranty covering certain faults or failures for a specified period.
A performance warranty guaranteeing that the battery will retain a minimum percentage of its original usable capacity.
These aren’t necessarily the same thing, so it’s important to read the precise terms supplied with your battery.
A battery might, for example, be advertised with a 10-year warranty and a guarantee that it will retain at least 80% of its original capacity at the end of that period.
If it had 13.5kWh of usable storage when new, 80% capacity retention would leave it with approximately 10.8kWh after 10 years.
However, that performance promise may be subject to an additional operating limit.
This is where throughput enters the picture.
🎥 Prefer video? Check out our YouTube video explaining domestic battery warranties:
Batteries age in two different ways
Every battery experiences two types of ageing.
Calendar ageing
Calendar ageing happens simply because the battery gets older.
Even if a battery were installed and rarely used, its cells would still gradually degrade.
Temperature, chemistry and the amount of time it spends at different states of charge can all influence this process.
Cycle ageing
Cycle ageing is caused by charging and discharging the battery.
Each time lithium ions move through the cells, they create a tiny amount of physical and chemical stress.
One charge or discharge makes virtually no noticeable difference, but the effect accumulates over thousands of cycles.
A 10-year-old battery that has worked hard every day has therefore experienced both calendar ageing and cycle ageing. A battery of the same age that has barely been used has mainly experienced calendar ageing.
That is why manufacturers may place limits on both the battery’s age and its total usage.
What is a battery cycle?
One complete battery cycle means discharging the equivalent of 100% of the battery’s usable capacity and then charging it again.
That doesn’t have to happen in one uninterrupted session.
For example, using 50% of the battery today and another 50% tomorrow would add up to approximately one equivalent full cycle.
Manufacturers sometimes advertise cycle-life figures such as 4,000 or 6,000 cycles. These are useful as a general indication of durability, but real homes rarely operate in perfect, easily counted cycles.
Your solar panels might charge the battery in the morning, the kettle could partially discharge it, passing clouds might reduce generation, and an export tariff could send some of the remaining energy to the grid.
This makes individual cycles messy to measure.
What is battery throughput?
Energy throughput is the total quantity of energy that has passed through a battery over its working life. It is usually measured in kilowatt-hours (kWh) or megawatt-hours (MWh).
The battery management system can record this figure continuously. It doesn’t matter whether the energy moved through the battery during one large discharge or hundreds of smaller ones - the total keeps climbing.
Think of it as the battery’s odometer.
Counting cycles would be like trying to measure a car’s usage by counting how many times its fuel tank was filled.
Throughput is more like recording the total mileage: it provides a much clearer picture of how intensively the system has been used.
Some battery warranties therefore apply until the first of two limits is reached:
The stated warranty period, such as 10 years.
The maximum permitted energy throughput.
Exactly what happens after that limit is reached depends on the manufacturer’s wording. It may affect a capacity-retention guarantee without necessarily ending every form of product or fault cover, so always check the complete warranty rather than relying on a headline summary.
Could you reach the throughput limit before 10 years?
Yes, theoretically - but it depends heavily on the battery and how you use it.
The video accompanying this guide examined several warranty documents and calculated how long their throughput allowances could last if the battery completed the equivalent of one full cycle every day.
Battery | Throughput allowance per kWh of capacity* | Approximate time at one full cycle per day |
BYD Battery-Box | 2.52MWh per kWh | 6.9 years |
AlphaESS | 3.11MWh per kWh | 8.5 years |
Sigenergy SigenStor | 3.114MWh per kWh | 8.5 years |
*Figures discussed in the accompanying video. Warranty documents can change and may vary by product, installation date, application and market. Check the current warranty supplied with your specific system before making a decision.
These calculations represent intensive, highly consistent usage. Most households won’t discharge 100% of their battery’s nominal capacity every day.
Batteries usually keep a small amount of their total cell capacity inaccessible to protect the cells. Household demand and solar generation also vary, producing partial rather than complete daily cycles.
As a result, a typical solar self-consumption system may take considerably longer to reach its throughput allowance.
How to estimate your own battery’s throughput period
If the warranty gives an allowance in kilowatt-hours of throughput for every kilowatt-hour of battery capacity, use:
Estimated years = throughput allowance per kWh ÷ 365
For example:
2,520kWh per kWh ÷ 365 = 6.9 years
That calculation assumes the equivalent of one full cycle every day.
If you typically use 70% of the battery’s usable capacity each day, an approximate calculation would be:
Estimated years = throughput allowance per kWh ÷ (365 × 0.7)
Using the same example:
2,520 ÷ 255.5 = 9.9 years
This is only a guide. Actual warranty calculations can depend on whether the manufacturer measures charge throughput, discharge throughput or aggregate throughput, as well as its definition of usable capacity.
When should homeowners pay particular attention?
Throughput is less likely to be a problem for a battery used mainly to store excess solar energy and power the home overnight.
It becomes more important when the battery is deliberately cycled more often or more deeply.
Dynamic electricity tariffs
A time-of-use tariff may encourage your battery to charge when electricity is cheap and discharge when prices rise.
This can improve the financial return from the system, but it also adds to its lifetime throughput.
Energy trading and export automation
Some systems automatically buy, store and export electricity according to changing market prices.
If the battery is charged and discharged aggressively, it could complete the equivalent of more than one cycle on particularly active days.
Virtual power plants and grid services
A virtual power plant - or VPP - allows an operator to use participating home batteries to support the electricity network.
Homeowners may receive payments or bill credits in return, but frequent grid-led charging and discharging can increase battery usage.
Before enrolling, check whether the scheme’s potential income outweighs the value of the additional degradation and whether participation affects the manufacturer’s warranty.
Heavy daily load shifting
Homes with heat pumps, electric vehicles or high electricity consumption may regularly use most of their available battery capacity.
This doesn’t automatically make a battery unsuitable, but the throughput allowance should be part of the buying decision.
Is the Tesla Powerwall 3 different?
Tesla’s European Powerwall warranty takes a different approach for specified household applications.
For solar self-consumption, time-based control and backup use, the warranty lists unlimited cycles and an 80% energy-retention figure after 10 years.
A 37.8MWh aggregate-throughput limit applies when the Powerwall is used for applications outside the categories listed in the warranty.
The Powerwall has an initial stated energy capacity of 13.5kWh. At one equivalent full cycle per day, it could process around 49MWh over 10 years - more than the 37.8MWh allowance used for Tesla’s “other application” category.
That distinction matters: Tesla allows time-based household control without applying the normal throughput cap, provided the battery is used within the applications and conditions defined in its warranty.
As with any battery, homeowners should read the warranty applicable to their country, installation date and intended use. Tesla’s current UK owner documents and warranty terms are available on its website.
Does this mean 10-year battery warranties are misleading?
Not necessarily.
Manufacturers need a reasonable way to distinguish between an ordinarily used home battery and one subjected to unusually intensive operation. A time-and-throughput structure can be a legitimate way to do that.
The problem is visibility.
A large “10-year warranty” headline is easy to understand. A throughput allowance hidden several pages into a technical PDF is not.
For a typical household using its battery for solar self-consumption and ordinary load shifting, the advertised time limit will probably remain the more relevant one.
However, changing energy tariffs and grid-service schemes mean tomorrow’s batteries could be used much more intensively than yesterday’s.
That makes the small print increasingly important.
Five questions to ask before buying a home battery
Before choosing a system, ask your installer:
Does the warranty include a throughput or cycle limit?
What exactly happens when that limit is reached?
Is the limit based on charging, discharging or aggregate energy throughput?
Are dynamic tariffs, energy trading and VPP participation permitted?
What capacity-retention percentage is guaranteed at the end of the warranty?
Ask for the complete warranty document - not only the product brochure - and keep a copy of the version that applied when your battery was installed.
The bottom line
A battery advertised with a 10-year warranty may also carry a usage-based limit.
Most households using a battery for normal solar self-consumption are unlikely to encounter serious problems.
But if you intend to cycle it heavily through dynamic tariffs, automated trading or grid services, throughput deserves just as much attention as capacity, power output and price.
The best battery isn’t simply the one with the longest headline warranty. It’s the one whose warranty fits the way you plan to use it.
If you’re considering solar and battery storage, Heatable can design a system around your home, electricity use and preferred tariff.
Book a free design call with one of our experts to compare your options and understand the warranty before you buy.
Next Steps For Your Battery Journey:
When planning to install battery storage for your home, there are several important factors to consider. Make sure to refer to the following guides to help you make informed decisions:
To dive deeper into these topics, head over to our advice section, check out our YouTube channel for informative videos, or read a customer case study to see how others have benefited from their battery installation.
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Warranty terms, product specifications and tariff arrangements can change. This guide is general information and does not replace the warranty supplied by the manufacturer.
